The document summarizes the spread and impact of ostreid herpesvirus 1 microvariant (OHV-1 μVar), also known as Pacific oyster mortality syndrome (POMS), on oyster farms in Europe, New Zealand, Australia, and Japan between 2008-2012. It notes that the virus caused high mortality rates when it first emerged in Europe in 2008 and continued to spread and cause outbreaks in subsequent years. Similar outbreak patterns were observed in New Zealand and Australia between 2010-2011. Limited information is available about impacts in Japan. The virus appears able to persist at low levels in environments before triggering new outbreaks under suitable water temperature conditions.

3. } 2008 First mortality event caused by OHsV-1uVar
Wide spread mortality (50 – 90%) and farmers spread the
virus to all parts of Europe through stock & equipment
translocation
} 2009 saw further small infection to England & Ireland.
France mortality still high but not as severe as 2008
} 2010 varying rates of infection similar to 2009 with 40 –
80%
} 2011 similar results to 2009 & 2010, virus appears to have
taken up residency
} 2012 outbreaks of POMS reported in France and England in
early August. Volumes of mortality yet to be confirmed

4. } Early 2010, mortality event infecting much of the
North Island. Mortality up to 80+% in some bays.
} Late 2010 saw a new round of mortality events but
not as severe as earlier in the year.
} 2010 POMS detected in the South Island but no
mortalities. The fact that the virus has not
materialised into mortalities is assumed due to the
cooler water temperatures compared to the North
Island
} 2011 saw smaller infection rates and mortalities were
lower than 2010

5. } 2010 – Large mortality event in Georges River
NSW. Death rate of 90+% of all farmed & wild
Pacific Oysters. Further deaths confirmed in
Sydney Harbour
} 2011 – a second wave of POMS but over 2 or
3 events. Inconsistency possibly caused by a
wet year with varying water temperatures &
salinity.
} 2012 - ??

6. } Reports emerging of slightly different version
of POMS strain found in Japan. Mortality rates
are unknown as information is being well
controlled by government.
} Growers in Hiroshima Bay (Japan’s largest
producing region) are not seeing any
mortality events
} Very little communication from Asia in
relation to POMS

7. } Australian delegation to France heard from IFREMER
that New Zealand frozen samples stored from 2006
had shown positive tests to POMS.
} New Zealand confirmed that frozen samples stored
from 2005 also had positive tests to POMS, but no
mortalities until 2010
} New Zealand had un-explained mass mortality event
in late 1990’s. POMS virus was unknown at that time
} There is growing evidence that POMS is not passed on
through vertical transmission, more likely horizontal

8. } Needs water temperature over 17°c to trigger
virus
} The most efficient way to spread the virus is
through stock & equipment translocation
from infected bays
} 2011 & 2012 testing program has found no
POMS in TAS & SA